Tree-crop interactions in hedgerow intercropping with different tree species and tea in Sri Lanka: 2. Soil and plant nutrients

The primary objective of the present study was to determine the capacity for soil fertility improvement in hedgerow intercropping systems (HIs) involving six different hedgerow species (Calliandra calothyrsus Meissner, Senna [Cassia] spectabilis (DC.) H. Irwin and Barneby, Euphatorium innulifolium (R.M. King and H. Rob.) H.B.K., Flemingia congesta Aiton F., Gliricidia sepium (Jacq.) (Kunth.) Walp. and Tithonia diversifolia (Hemsi.) A. Gray) and tea (Camellia sinensis (L.) O. Kuntz) on sloping terrain in the high rainfall zones of Sri Lanka. Incorporation of hedgerows and addition of their prunings as mulch decreased topsoil bulk density and increased organic matter content and cation exchange capacity. In the majority of mulched HIs, most of the essential soil nutrients, with the exception of phosphorus, were higher than in sole tea crops. In HIs involving all tree species, the mulched treatment had significantly greater soil nutrient contents than the respective unmulched treatment. When prunings were not added as mulch, there was evidence of competition for nutrients between the tea bushes and hedgerow species. The amounts of nutrients added through hedgerow prunings exceeded the recommended K requirement of tea, but were lower than the N and P requirements. In a majority of HIs, the amounts of nutrients exported as tea yield were lower than in the control under both mulched and unmulched conditions. It is concluded that incorporation of contour hedgerows has the potential to regenerate soil fertility and sustain tea yields on sloping terrain in Sri Lanka, when prunings are added, as mulch.